Respirator for Face Mask
It is actually a simple product with a big impact. The material in most of the breathing valves used is made of durable PVC plastic at the outside and an elastic soft flap at the inside. While inhaling, the flap closes tightly to ensure no particles flow into the mask and your body. But at exhaling, the flap opens up to let the moist air go out. At the same time, the soft flap still makes sure that none of the fine particles enter your mask.
This process ensures a smoother breathing experience, at exhaling but not inhaling. The humidity in your mask will find an easier way out of your mask. So, your face and your mask are meant to stay drier and cleaner, if you have a mask with a breathing valve.